Gas turbine control with prewhirl of air entering the compressor

ABSTRACT

A vehicle turbine of the gas-coupled type propels the vehicle through a change-speed transmission. To reduce vehicle acceleration time with an acceptable penalty with respect to fuel consumption, the compressor of the engine has variable inlet guide vanes which are shifted into a positive prewhirl angle at idling speeds when the transmission is shifted into a drive condition. Thus the engine gas generator has a low speed idle, with axially oriented guide vanes and normal air entrance, when the transmission is in neutral, and a high speed idle with positive prewhirl when the transmission is in drive condition. Also, the vanes are shifted at full speed of the gas generator to provide negative prewhirl and thus reduce the engine speed corresponding to maximum power output. Because of the higher idle and lower maximum speeds, the acceleration time of the gas generator, and thus of the power turbine, is reduced. Because positive prewhirl reduces compressor pressure ratio at the high speed idle, the power turbine does not have an undue tendency to cause creep of the vehicle in the high speed idle.

United States Patent Amann et a1.

[ 1 Apr. 25, 1972 54] GAS TURBINE CONTROL WITH FOREIGN PATENTS ORAPPLICATIONS 2 AIR ENTERING THE 693,227 6/1953 Great Britain ..60/39.29

[72] Inventors: Charles A. Amann, Bloomfield Hills; Erik Pnmary '""f fGordon H. Rucins, Sterling Heights, both of Mich Attorney-PaulFitzpatrick and Jean L. Carpenter [73] Assignee: General MotorsCorporation, Detroit, [57] ABSTRACT Mlch' A vehicle turbine of thegaseoupled type propels the vehicle [22] Filed: Sept. 2, 1969 through achange-speed transmission. To reduce vehicle ac- 1 celeration time withan acceptable penalty with respect to fuel [211 APPI' 854,651consumption, the compressor of the engine has variable inlet guide vaneswhich are shifted into a positive prewhirl angle at 52 vs. C]..60/39.29, 60/39.16 d i Speeds when e transmission is Shifted into adrive 9 51 Int. Cl. ,.F02c 9/14 F T engme g generator has a low-SpeedIdle 581 Field of Search .,60/39.29,39.02, 3903,3925, Wlth anally e e gnes and normal an entrance, 60/3916 'when the transmission is inneutral, and a high speed idle with positive prewhirl when thetransmission is in drive condition. I 56] References Cited Also, thevanes are shifted at full speed of the gas generator to provide negativeprewhirl and thus reduce the engine speed UNITED STATES PATENTScorresponding to maximum power output. Because of the higher idle andlower maximum speeds, the acceleration time 3 .093,010 6/1963 Spreitzer..74/864 of h gas generator, and thus Ofthe power turbine, is reduced,3.1 16,605 1/1964 Amann ..60/39.16 X Because positive prewhirl reducescompressor pressure ratio 3.209,537 10/1965 MOCk ..60/39.25 X at the hispeed idle, the power turbine does not have an 3267674 8/1966 Couman- Xundue tendency to cause creep of the vehicle in the high speed 2,737,0173/1956 Feiss ..60/39.03 id]e 2,950,857 8/1960 Williams ..60/39.29 X3,500,637 3/1970 Toy ..60/39.03 12 Claims, 3 Drawing Figures Q d9 2 zz j20 1 W 7 .i [1 1 7 (I 3,4 p 1 24 e a g TRANSMISSION LOAD I, ,1 I g".4n|\\\\ LII/Ms 5y I a 51 30 a. Q 53 l 1 M st SPEED zi TRANSDUCER a? 3n51 a GAS TURBINE CONTROL WITH PREWI-IIRL OF AIR ENTERING THE COMPRESSORThis invention relates to gas turbine power plants, to make them bettersuited to the requirements for power plants for automotive vehicles. Itis particularly directed to improving the acceleration characteristicsfrom idle to medium or full load of a gas turbine powering a vehicle.

Along with their many advantages, gas turbines have significantdisadvantages for vehicle propulsion as compared, for example, togasoline reciprocating engines and diesel engines.

One of these disadvantages is relatively high fuel consumption at idle,particularly with relation to that of the diesel engine. Anotherdisadvantage is a substantial time lag between idle and full power whichis undesirable in stop and go driving. It is, thus, highly desirable tofind means to improve the acceleration and the part load fuelconsumption characteristics ofsuch engines.

The acceleration characteristics of the usual gas turbine engine can begreatly improved by increasing the idle speed of the engine. In theordinary gas-coupled engine, the minimum satisfactory gas generator idlespeed is somewhere near fifty percent of the speed at full power. Bystepping up the idle speed to, say, 75 percent, the time required forthe gas generator to accelerate to full power output is greatly reduced.As a matter of fact, it is possible to idle the engine at 100 percentgas generator speed by braking the power turbine. However, such highspeed idling greatly increases the fuel consumption while the vehicle isstationary.

It is also desirable, for convenience in driving the vehicle, to havethe torque of the power turbine sufficiently low when the gas generatoris idling that is not necessary to hold the vehicle brakes engaged toprevent vehicle creep. It is desirable to have a characteristic similarto that of a gasoline engine with a torque converter which idles at aspeed sufficiently low that the torque converter transmits too small atorque to move the vehicle.

The principle ofthis invention is based upon the conclusion that theidle speed of the gas generator may be substantially increased, withoutincreasing the gas horsepower which tends to drive the power turbine, byimparting substantial positive prewhirl to the air entering thecompressor. Positive prewhirl is a tangential component of air velocityin the direction of rotation of the compressor. Also, to minimize wasteof fuel when the vehicle is not in the ready condition for operating,this prewhirl is eliminated when the transmission is put into neutral orpark conditions and the engine is then allowed to idle at a low speedidle. Also, the speed of the gas generator at maximum gas horsepoweroutput is reduced somewhat by imparting negative prewhirl (that is,whirl opposite to compressor rotation) to the air entering thecompressor when operating near maximum gas generator speed. By thesemeans, a reduction of approximately one-third in the difference betweenready idle and full power gas generator speeds may be achieved, with acorresponding very substantial reduction in acceleration time,particularly since the acceleration of the gas generator through thelower part of its speed range is slower than through the higher part ofits speed range.

The prewhirl may be controlled by variable-setting inlet guide vanes inthe engine compressor.

The nature of the invention and its advantages will be clear to thoseskilled in the art from the succeeding detailed description of thepreferred embodiment of the invention and the accompanying drawings.

F IG. 1 is a schematic diagram of a vehicle gas turbine installationincluding controls according to the invention.

FIG. 2 is a frontal view of the engine compressor inlet.

FIG. 3 is a graphical representation of operating conditions atdifferent speeds and vane angle conditions.

FIG. 1 illustrates schematically a gas-coupled gas turbine engine which,as is customary, includes a dynamic compressor 7, a combustion apparatus8, and a gas generator turbine 10. Turbine l drives compressor 7 througha shaft 11, and compressed air flows from the compressor 7 to thecombustion apparatus 8 to which fuel is also supplied through a fuelline 12. The fuel is burned in the compressed air and the resultingcombustion products flow to turbine 10 to energize it. The exhaust fromturbine 10 flows to a power turbine 14 and then to exhaust.

As illustrated, the engine is non-regenerative although, of course, aregenerator may be included without affecting this invention. There aremany structural disclosures of such engines, including those in U.S. PatNos. 2,972,230 to Conklin et al., for Automobile Gas Turbine, 3,1 16,605to Amann et al., for Regenerative Gas Turbine, and 3,267,674 to Collmanet al., for Regenerative Gas Turbine. The power turbine 14, whichrotates independently of the gas generator turbine 10, drives through apower output shaft 15 into a transmission or change gear box 16 of anysuitable type. The transmission drives a load 18 which, in the preferredenvironment of the invention, is the driving wheels of a motor vehicle.

The gas turbine engines referred to above do not include variable inletguide vanes to vary the prewhirl of the air entering the compressor, butsuch are well known. Structural disclosures of variable inlet guide vanearrangements may be found in U.S. Pat. Nos. 2,862,654 to Gardiner forVariable Pitch Guide Vanes and 2,857,092 to Campbell for VariableCompressor Vanes. As illustrated schematically in FIG. 1, the compressorcomprises a converging annular inlet 19 and an inlet guide vanestructure 20 including an annular cascade of vanes 22, each vane beingrotatable about an axis extending radially of the guide vane ring andbeing movable by an arm 23. The arms 23 are all pivotally connected toan actuating ring 24 encircling the compressor. Ring 24 may be rotatedby actuating means to be described to vary the setting or angle of theinlet guide vanes.

The inlet structure is shown more structurally in FIG. 2 which alsoillustrates a center bullet or fairing 26 of the inlet, and a number ofvariable setting vanes 22. The compressor 7 may be axial-flow or may becentrifugal as in the patents referred to above.

In the described embodiment of the invention, the ring 24 is actuated bya three-position hydraulic actuator 27 which comprises two double-actinghydraulic cylinders fixed together in tandem with one piston rodextending from each end of the actuator. Thus, one cylinder 28 hasreciprocable therein a piston and rod assembly 30 and the other cylinder31 has therein a piston and piston rod assembly 32, the piston rod 32being connected to a fixed structure at 34. Piston rod 30 is suitablyconnected by means such as a pin 35 to the actuating ring 24. As appliedhere, the actuator 27 can move the ring 24 to three positions; one whenboth pistons are at the inner ends of the cylinders, one when piston 30is at the outer end, and one when both pistons are at the outer ends ofthe cylinders. The particular structure of the actuator 27 is notmaterial to this invention, since any suitable three position actuatingdevice may be used or, if desired, a multi-position actuator device. Onesuitable type of actuator is described in detail in Short et al., U.S.Pat. No. 2,893,353 for Three Position Actuator Cylinder.

The transmission 16 is a suitable form of change speed gear to adapt thetorque characteristics of the engine to the requirements of the load.The details of the transmission are immaterial to this invention but itpreferably is a power-shift transmission and one in which thetransmission controls include a neutral position and at least one driveposition. One example of such a transmission is that disclosed inSpreitzer et al., U.S. Pat. No. 3,093,010. As illustrated schematicallyin the drawing, transmission 16 includes a control lever 37 which may bemanually operated and which has a neutral position indicated by N and atleast one drive position indicated by D. The transmission includes anormally open switch 36 which is closed whenever the control is moved tothe drive position. Alternatively, switch 36 could be a normally closedswitch which is held open only when the control lever is in neutralposition.

Switch 36 controls the supply of actuating fluid to the actuator 27 inconnection with means responsive to the speed of the gas generatorturbine indicated as a speed transducer 38 driven from the gas generatorshaft 11 through gearing and accessory drive shaft 39. This can be anysuitable device effective to move an output element as a function of gasgenerator speed. The transducer 38 controls a normally closed switch Aand a normally open switch B. Switches A and B control twosolenoid-actuated reversing valves 40 and 42 which control the supply ofactuating fluid to the cylinders 28 and 31 of actuator 27. In theillustrated embodiment, the fluid is hydraulic fluid supplied from areservoir 43 under pressure by a pump 44 which may, for example, bedriven from the gas generator shaft 11, and may also, if desired, be thelubricating pump of the engine.

As illustrated, the pump 44 supplies fluid through a branch line 46 tovalve 40 and through a branch line 47 to valve 42.

These valves are connected back to the reservoir by return lines 48 and50, respectively. These valves 40 and 42 simply serve to connect theactuating cylinders either normally or reversely to the pump to causethe piston to be driven to one end or the other of the cylinder 28 or 31in which it reciprocates.

The fluid pressure system could, if desired, be an air pressure system,and specifically the actuator of the Short et al. patent referred toabove is adapted for actuation by compressed air.

The speed transducer 38 moves a switch operating plunger 51 which bearslugs which actuate the switches A and B. In the particular embodimenthere described, normally closed switch A is opened by the plunger 51 atapproximately 58 percent full gas generator speed and remains open athigher speeds, and switch B remains open until the gas generator reachesapproximately 95 percent full speed, at which point it is closed andremains closed at higher speeds. A suitable energizing circuit for thesolenoid valves is indicated by a circuit from ground through a battery54 and a positive line 55 to switch B by which it is connected toenergizing line 56 for solenoid valve 42, which is connected to ground.When the solenoid valve 42 is not energized, the pressure line 47 isconnected through a line 58 to hold the piston and rod assembly 30 inthe short cylinder 28 extended and the outer end of the cylinder isconnected through line 59 and valve 42 to the return line 50. The inletvanes 22 are then set at prewhirl. When the solenoid is energized, theconnections to lines 58 and 59 are reversed and the piston 30 is pulledinward to shift the ring 24 and move the vanes to the minus setting.Thus, the vanes are moved to this minus 20 setting at top gas generatorspeed, above about 95 percent rated.

Solenoid valve 40 is likewise shown in its deenergized condition, inwhich fluid is conducted from pump output line 46 through a line 60 tothe outer end of cylinder 31 to hold the piston and rod assembly 32retracted into the cylinder and the inner end of the cylinder 31 isconnected through a line 62 and valve 40 to the return line 48. Thevalve is shown deenergized because, although switch A is shown closed,switch 36 is open. Now, if the transmission control 35 is shifted into adrive position, switch 36 is closed to complete a circuit from line 55through switch 36, line 63, switch A, which is assumed closed, to thesolenoid valve 40 to reverse the connection to cylinder 32 to extend thepiston and rod 32 and move the vanes 22 to the plus 60 degrees prewhirlposition.

As previously stated, switch A is closed below approximately 58 percentgas generator speed and opens at 58 percent speed to reverse theconnection to cylinder 31 of actuator 27 and thus restore the vanes tothe zero prewhirl position. This sequence of events is indicated by theline M on the chart of FIG. 3 which, as will be seen, indicates thevanes as being at plus 60 below 58 percent gasifier speed, shifting to 0at 58 percent, remaining at 0 to 95 percent, then shifting to minus 20from 95 to 100 percent gas generator speed. The broken line N indicatesthe override by the switch 36 which, when it is open, causes the vanesto return to the zero degrees position for normal low speed or standbyidle operation of the power plant.

As previously stated, the purpose of the positive prewhirl is to allowfaster idle operation of the gas generator without sufficient gas poweroutput to the power turbine to cause undesirable tendency of the vehicleto creep. The gas generator will not automatically speed up because ofthe change of inlet vane angle if it is controlled, as is usually thecase, by a governor. Gas turbines ordinarily have a fuel control whichprovides for control of power output and assures safe operation of theengine without surge, overspeed, overheating, flameout, and otherdisturbances of the operation. One element of the fuel control system ofthe usual gas-coupled gas turbine engine is an adjustable governor whichcontrols the speed of operation of the gas generator and thus its gaspower output to the power turbine. Such a control ordinarily alsoincludes some sort of speed limiting governor on the power turbine whichacts to override the gas generator governor and reduce gas horsepowerwhen the power turbine tends to overspeed, although this is not alwaysnecessary. Various such arrangements of fuel controls are known; one isdisclosed in Zeek US. Pat. No. 3,203,176 for Engine Governor, anotherin'Flanigan et al., US. Pat. No. 2,976,683 for Gas Turbine Fuel Systemwith Regenerator Temperature Compensation, another in Bevers US. Pat.No. 3,332,232 for Fuel Control.

In the preferred embodiment illustrated herein, the gas turbine fuelcontrol omits the power turbine governor or has a fixed setting powerturbine governor, and the control to implement the invention is effectedby a gas generator governor in the fuel control. Referring to FIG. 1, afuel control 64 is supplied with fuel under pressure from any suitablesource through a line 67 and meters fuel to the engine through the line12 extending to the combustion apparatus 8. The control 64 receives aninput of gas generator speed from shaft 39 and suitable transmissionmeans illustrated by the gearing and shaft 70. It also receives an inputof power turbine speed for the power turbine overspeed governor througha shaft 71 geared to the power turbine output shaft 15. Additionally,the control 64 receives an input of desired power output or gasgenerator speed which is transmitted from a control indicated as a footthrottle pedal 72 through linkage 74 to a swinging input arm 75 on thefuel control. Arm 75 may be considered to be biased counterclockwise orin the direction of decreasing speed and power by a tension spring 76.The minimum speed position of arm 75 is determined by a movable stop 78which has a position of rest in which the arm 75 moves to the minimumpower or standby idle position and a second position in which the arm 75is held farther in the counterclockwise direction to call for a higheridle speed. The variable stop 78 is moved to the high speed position bysuitable means such as solenoid 79 energized from line 63 whenever thetransmission switch 36 is closed.

Thus, the engine may operate at a low speed idle with the inlet vanes at0 and the transmission in neutral. When the transmission is shifted to adrive condition, the vanes are shifted to 60 positive prewhirl as shownon the line M in F lG. 3. At the same time, the stop 78 is energized toboost the speed setting of the gas generator governor to cause it to runjust below the 58 percent speed point.

As the foot throttle 72 is actuated to cause the vehicle to move off,the governor setting is raised and the gas generator speeds up, causingthe speed transducer 38 to open switch A and thereby put the inlet guidevanes back to the zero prewhirl position. Finally, as the power isincreased and the engine accelerates toward maximum gas generator speed,the switch B is closed and the vanes are given a minus 20 setting forfull power operation.

The effect of this may be appreciated more clearly from the curvesindicated as X, Y, and Z in FIG. 3. Curve X represents the operation ofthe engine with minus 20 prewhirl through the speed range from idlebelow 50 percent speed to percent speed at full power. Note that gashorsepower supplied to the power turbine increases from about 8 percentto about 100 percent over this speed range. The curve Y indicatesoperation with the vanes set at in which case the power output is lowerand finally increases to about 80 percent normal at full speed. Thecurve Z indicates the result of operation with the 60 positive prewhirlwith the result that the power output is very much less than the valueassociated with normal operation of the engine. Thus, the higher idlespeed may be maintained without generation of sufficient gas horsepowerto create objectionable creep problems in the vehicle, since gashorsepower and therefore power turbine torque remain low.

The detailed description of the preferred embodiment of the inventionfor the purpose of explaining the principles thereof is not to beregarded as limiting the invention, as various modifications may be madeby the exercise of skill in the art.

We claim:

1. A vehicle power plant comprising, in combination, acompressor-combustor-gas turbine gas generator, a power turbineenergized by the gas generator, and a transmission coupling the powerturbine to the vehicle for vehicle propulsion, the transmission having aneutral condition and a powertransmitting condition; and means effectiveto improve vehicle acceleration relative to idling power turbine torquetending to cause creep of the vehicle comprising means for impartingsubstantial positive prewhirl to air entering the gas generatorcompressor when the gas generator is idling and the transmission is inthe power-transmitting condition.

2. A power plant as recited in claim ll including means for increasinggas generator speed when the positive prewhirl is imparted.

3. A power plant as recited in claim 2 in which the lastrecited meansincludes a variable-speed governor and means to increase the governoridling setting when the transmission is in the power-transmittingcondition.

4. A power plant as recited in claim 1 including also operator-operablemeans for controlling gas generator speed and means coupled to theoperator-operable means for increasing the minimum gas generator speedwhen the transmission is in the power-transmitting condition.

5. A power plant as recited in claim 1 in which the lastrecited meansincludes means responsive to transmission condition and means responsiveto gas generator speed.

6. A power plant as recited in claim 5 including also means forincreasing the minimum gas generator speed responsive to the meansresponsive to transmission condition and the means responsive to gasgenerator speed.

7. A power plant as recited in claim 1 including also means forimparting substantial negative prewhirl to air entering the compressorwhen the gas generator is operating near maximum rated speed.

8. A power plant comprising, in combination, a gas turbine gasgenerator, a power turbine, and a power transmission having a neutralcondition, the gas generator including a compressor with adjustableprewhirl vanes; first control means responsive to gas generator turbinespeed effective to vary the adjustable vanes so as to vary prewhirl frompositive at low gas generator speeds to negative at high gas generatorspeeds; and second control means responsive to setting the transmissionin neutral condition effective to override the first control means andeliminate prewhirl when the transmission is in neutral.

9. A power plant as recited in claim :8 including means for increasinggas generator speed when the positive prewhirl is imparted.

10. A gas turbine power plant comprising, in combination, a gas turbinegas generator including a compressor, combustion apparatus supplied bythe compressor, and a first turbine supplied by the combustion apparatuscoupled to drive the compressor, the compressor having variable settinginlet guide vanes for imparting prewhirl to air entering the compressor;a second turbine energized by the gas generator; power trans missionmeans coupling the second turbine to a load, the power transmissionmeans including means for setting it into a neutral condition and intoat least one drive condition; means responsive to the transmissionsetting means and to gas generator speed effective to set the inletguide vanes to a position to impart substantial positive prewhirl whenthe transmission setting is other than neutral and gas generator speedis below a high idle limit; and means responsive to gas generator speedeffective to adjust the inlet guide vanes to a position to impartsubstantial negative prewhirl when gas generator speed is near maximumrated speed.

11. A power plant as recited in claim 10 including means for increasinggas generator speed when the positive prewhirl is imparted.

12. A power plant as recited in claim ll in which the lastrecited meansincludes a variable-speed governor and means to increase the governoridling setting when the transmission is in the drive condition.

1. A vehicle power plant comprising, in combination, acompressor-combustor-gas turbine gas generator, a power turbineenergized by the gas generator, and a transmission coupling the powerturbine to the vehicle for vehicle propulsion, the transmission having aneutral condition and a power-transmitting condition; and meanseffective to improve vehicle acceleration relative to idling powerturbine torque tending to cause creep of the vehicle comprising meansfor imparting substantial positive prewhirl to air entering the gasgenerator compressor when the gas generator is idling and thetransmission is in the powertransmitting condition.
 2. A power plant asrecited in claim 1 including means for increasing gas generator speedwhen the positive prewhirl is imparted.
 3. A power plant as recited inclaim 2 in which the last-recited means includes a variable-speedgovernor and means to increase the governor idling setting when thetransmission is in the power-transmitting condition.
 4. A power plant asrecited in claim 1 including also operator-operable means forcontrolling gas generator speed and means coupled to theoperator-operable means for increasing the minimum gas generator speedwhen the transmission is in the power-transmitting condition.
 5. A powerplant as recited in claim 1 in which the last-recited means includesmeans responsive to transmission condition and means responsive to gasgenerator speed.
 6. A power plant as recited in claim 5 including alsomeans for increasing the minimum gas generator speed responsive to themeans responsive to transmission condition and the means responsive togas generator speed.
 7. A power plant as recited in claim 1 includingalso means for imparting substantial negative prewhirl to air enteringthe compressor when the gas generator is operating near maximum ratedspeed.
 8. A power plant comprising, in combination, a gas turbine gasgenerator, a power turbine, and a power transmission having a neutralcondition, the gas generator including a compressor with adjustableprewhirl vanes; first control means responsive to gas generator turbinespeed effective to vary the adjustable vanes so as to vary prewhirl frompositive at low gas generator speeds to negative at high gas generatorspeeds; and second control means responsive to setting the transmissionin neutral condition effective to override the first control means andeliminate prewhirl when the transmission is in neutral.
 9. A power plantas recited in claim 8 including means for increasing gas generator speedwhen the positive prewhirl is imparted.
 10. A gas turbine power plantcomprising, in combination, a gas turbine gas generator including acompressor, combustion apparatus supplied by the compressor, and a firstturbine supplied by the combustion apparatus coupled to drive thecompressor, the compressor having variable setting inlet guide vanes forimparting prewhirl to air entering the compressor; a second turbineenergized by the gas generator; power transmission means coupling thesecond turbine to a load, the power transmission means including meansfor setting it into a neutral condition and into at least one drivecondition; means responsive to the transmission setting means and to gasgenerator speed effective to set the inlet guide vanes to a position toimpart substantial positive prewhirl when the transmission setting isother than neutral and gas generator speed is below a high idle limit;and means responsive to gas generator speed effective to adjust theinlet guide vanes to a position to impart substantial negative prewhirlwhen gas generator speed is near maximum rated speed.
 11. A power plantas recited in claim 10 including means for increasing gas generatorspeed when the positive prewhirl is imparted.
 12. A power plant asrecited in claim 11 in which the last-recited means includes avariable-speed governor and means to increase the governor Idlingsetting when the transmission is in the drive condition.